In modern digital integrated circuits, particularly those fabricated according to the well-known complementary metal-oxide-semiconductor (CMOS) technology, many functional circuits internal to an integrated circuit rely upon current sources that conduct a stable current. Examples of such functional circuits include voltage regulators, differential amplifiers, sense amplifiers, current mirrors, operational amplifiers, level shift circuits, and reference voltage circuits. Such current sources are generally implemented by way of field effect transistors, with a reference voltage applied to the gate of the field effect transistor.
These circuits conventionally utilize a substantially constant current controlled by the current source. However, in connection with the present invention, it has been determined that it may be desirable to have the value of the current conducted by a current source to be different in different situations, such as if the performance of the individual integrated circuit as manufactured warrants. As will be described hereinbelow, in the generation of a reference voltage to be applied to an output buffer for control of a corresponding output driver, one may wish to optimize a tradeoff between low output impedance in the voltage reference circuit and DC current drawn by the voltage reference circuit.
It is therefore an object of the present invention to provide an adjustable current source.
It is another object of the present invention to provide such an adjustable current source where the current may be adjusted in stable fractions.
It is another object of the present invention to provide such an adjustable current source where the current may be selected permanently by way of fuse programming.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.